demonstrates how to implement a custom collection editor that allows items of a given type to be added to a collection at design time.
第二个则会示范如何实作自订集合编辑器,让指定型别之项目可以在设计阶段加入集合中。
third-party control developers can derive from this class to add items to the 「add item」 drop-down box in the collection editor or sub-property editor.